A 15-year-old boy has said he used a large length of fabric to strangle his 13-year-old girlfriend in a vacant pachinko parlor in Nakatsugawa, Gifu Prefecture, where she was found dead Friday, his lawyer said.
"After I strangled her, I hit her on the head with a stick," the boy told the lawyer, who met him Sunday.
Police earlier found a stick in the abandoned building. Other sticks and clothes were also found in a room on the third floor.
The boy was arrested late Friday on suspicion of killing his girlfriend, Nao Shimizu.
The boy is in his first year in high school. His name is being withheld because he is a minor. Police turned him over to prosecutors Sunday.
Investigators believe the youth strangled Shimizu after beating her on the head at around 6:30 p.m. Wednesday.
The boy was quoted as telling police, "I did it alone," and, "I intended to kill her."
Police searched the boy's home and several other locations Saturday, and found the victim's cell phone hidden in a drawer in the pachinko parlor after interrogating the boy.